Thought I would bring this to your attention.
Anyone on the 3 network in the UK.
They have had feel at home going for a while now, basically it allows you to use your phone in foreign countries ( 16 so far, USA, France, Sweden) as if you have never left the UK, so if you tariff allows unlimited data, calls ects you can use it with no costs incurred, I've used it in Sweden while working there last year, the good news is coming to Spain in April.
Read here.
http://store.three.co.uk/mobile/view/content/feelathome?site=m